The partnership would still continue. https://www.irs.gov/newsroom/questions-and-answers-about-technical-terminations-internal-revenue-cod... clarifies that no technical termination would happen in this scenario. 

I have to admit that the two "new" partners are also husband and wife might add to the possibilities. Is this a community property state? Possibly a Qualified Joint Venture and no need to file 1065. https://www.irs.gov/businesses/small-businesses-self-employed/election-for-married-couples-unincorpo...